Iwama is a post apocalyptic pokemon region, where desert makes up over 80% of the region -- if not the world itself -- and what remains struggles to survive.
However, thanks to the remnants of Kyogre's skeleton, one sole sea is still alive. People folk to this sea and the surrounding area, but many, wishing to fix the errors of the past, venture away from the waters, hoping that somewhere in the desert, they can take down the very being who started it all. In the post game of this campaign, Kyogre was brought back unsuccessfully; as such, it now decays once more in the sea. Groudon still reigns supreme, but to say that it's their fault is a misnomer -- in truth, it was human's greed for power that brought this world to how it is in the first place.